Abstract: This article mainly discusses the background，purpose and implementation of our CAD system for erection work in architecture．Our system can generate 3D construction structure drawing from traditional 2D drawings； let architects design erection subsystems，such as pumbing ventilation，and electricity directly in 3D space；help architects check the interference；and generate 2D work drawings that fit the needs of construction practice and implement the quantities count．This paper also describes the generation of 2D work drawings module in details．